ColorWorkDesk: Measuring Color with Spectrophotometers

Atlases: The First Attempts to Classify Color

Early studies of color that led to its initial classification relied on color atlases, such as the Munsell and NCS systems. These collections of color variations catalog colors based on lightness/darkness, tone, and saturation.

Over time, however, their use revealed several limitations, as they did not fully address the problem of subjective human perception. They quickly proved inadequate for meeting increasingly specific industrial requirements for color control and formulation.

This increased the need to measure color using instruments that reference objective colorimetric scales.

Illuminants: The First Constant in Color Measurement

According to wave theory, which explains the macroscopic phenomena of light, light is a set of electromagnetic waves classified by their wavelength.

Among all electromagnetic waves, the human eye can only perceive those with wavelengths between 400 and 700 nm. Evaluating the energy of each monochromatic source within this range constitutes the visible spectrum of color.

Different frequencies correspond to different colors: at one end of the spectrum, the highest frequencies correspond to violet, while the lowest frequencies correspond to red.

Every illuminant, whether natural or artificial (e.g., daylight, incandescent lamps, fluorescent lights, or LEDs), has its own constant energy distribution profile, which can be traced, quantified in the visible spectrum, and systematized in a universally valid table.

The Eye: The Second Constant in Color Measurement

To measure color objectively, only what the eye perceives should be considered, excluding the brain’s subsequent processing of optical signals, which introduces subjectivity.

The human eye, therefore, is a fundamental element in color measurement.

The eye quantifies perceived light using two types of receptors:

• Rods: Distributed across most of the retina, rods detect overall energy variations in the eye but cannot distinguish chromatic variations (black-and-white vision).
• Cones: Found in the fovea, a much smaller area near the center of the retina, cones are sensitive to chromatic intensity variations. There are three types of cones, each sensitive to blue, green, or red light.
• The colors we perceive are an additive combination of these three chromaticities.

The eye, through the iris—a diaphragm that can open and close—regulates the amount of incoming energy to achieve optimal vision conditions.

When the environment provides sufficient luminous energy, the cone-shaped angle formed by the iris diameter relative to the retina focuses most of the energy onto the fovea, and therefore the cones. In this case, vision is chromatic.

Once the optimal angle range (2°–10°) is estimated, the eye’s sensitivity to the three color components (blue, green, and red) can be calculated for each monochromatic source in the spectrum.

On average, this response to perceived colors can be considered constant and can be represented in a table.

Matter: The Only Variable in the Color System

Matter can absorb, transmit, or reflect light, scattering it in different directions inside and outside itself. It can also selectively absorb certain monochromatic sources normally emitted by a light source at equal energy levels and in a combined form.

If an object absorbs all light, it appears black. If it reflects all light—combining all monochromatic sources into a balanced, neutral set—it appears white (neutral light). If some or all light passes through the object, we perceive a degree of transparency.

By absorbing certain monochromatic sources relative to others, matter causes the physical phenomenon we perceive as color.

Thus, the only variable in the color system is the material of the object, which absorbs, reflects, or transmits varying percentages of light, generating the perceived color.

Numerically, it is possible to quantify how much of the incident white light is re-emitted by an object, providing a chromatic fingerprint.

Spectrophotometers: Different Measurement Modes

To obtain objective numbers that represent an object’s color, the interaction of the three elements (eye, light, and matter) must be considered, creating a universally recognized system.

This has resulted in tables that provide, for each nanometer in the spectrum, the energy levels of each natural or artificial illuminant.

Additionally, tables have been created to establish the average sensitivity of the eye to the three perceived chromatic energies for each nanometer in the spectrum, available for the two extreme angular ranges (2° and 10°).

Since the only variable is the material of the object, it is possible to determine its color starting from the material itself.

However, this requires an instrument like a spectrophotometer, which measures how a material and its specific properties interact with light.

By breaking light into various wavelengths within the visible spectrum, the instrument measures the intensity of each and records the data using photodiodes, allowing for precise measurements even at small wavelength intervals.

Quantifying the re-emitted intensities involves:

• Measuring the light hitting the material,
• Measuring the light re-emitted or transmitted by the material,Relating these two measurements for each point.

Consequently, the ratio between the light emitted by the illuminant and the light detected by the probe for each point between 400 and 700 nm generates a color fingerprint

As mentioned, the spectrophotometer can operate in two distinct modes:

• Reflection: Used when light does not pass through the object. The light hits the object and is reflected. The spectrophotometer probe collects and measures the reflected portion of this light beam.
• Transmission: Used for transparent objects when light passes through the object and is measured by a probe on the opposite side. The difference between the initial and measured energy also indicates the object’s transparency and the energy absorbed during the passage.

ColorWorkDesk Spectrophotometers: When Innovation Surpasses Tradition

Using the range of CWD benchtop and portable spectrophotometers allows the measurement of any material’s color in any situation.

These innovative instruments can work in both reflection and transmission modes, ensuring comprehensive color measurement coverage.

Choosing CWD spectrophotometers means utilizing high-performance tools seamlessly integrated with today’s digital technologies, such as apps, cloud platforms, and servers.

This distinct advantage makes a significant difference in the colorimetry industry, leaving behind outdated methods and offering faster, more precise, and complete color measurements.

Want to find the spectrophotometer best suited to your needs? Read “How to Choose a Spectrophotometer.”